Heat exchangers are used to transfer heat from a heat source or thermal mass into a fluid mass, such as the water in a swimming pool or spa. Heat exchangers can be used for example to either raise or lower the temperature of a fluid, for various applications, such as heating or cooling, and heat exchangers are used in various industrial applications such as automotive, air conditioning, power generation and shipping among others.
One application in which heat exchangers are suitable is in a heating system for a swimming pool which uses a heat pump system to maintain a warm temperature of the pool. The heat pump extracts heat from surrounding air and transfers it to the body of water in the pool.
Heat pump generally use less energy compared to gas or electric heaters to transfer heat to a body of water. Heat pumps transfer heat by circulating a substance called a refrigerant through a cycle of evaporation and condensation wherein the refrigerant alternately absorbs, transports, and releases heat during the cycle. The refrigerant absorbs heat from the surrounding air and it evaporates. The heated refrigerant is then compressed and channeled to the apparatus where it condenses and releases the heat it has absorbed to the body of water.
Conventional heat exchangers include housings that are typically constructed as one-piece housings whereby once the internal components are installed inside the housing, the housing is sealed permanently to prevent water leakage during usage. Typically the housing is manually sealed through a plastic welding process. Therefore in the event of any damage or malfunction of the internal components, the whole heat exchanger is typically replaced.
Disadvantageously, unsealing the housing may damage the housing, such that cleaning, servicing or replacing the internal components is generally not feasible with existing swimming pool heat exchangers.
The housing of existing heat exchangers used for heating swimming pools is typically constructed from Engineering Plastic such as glass reinforced polypropylene which provides lower heat and chemical resistance. To construct the housing, individual parts of the housing are machined and subsequently attached together, for example, with plastic welding to define a complete unit. This construction process is relatively labour intensive and is still prone to leakage as the precision of the sealing may not be standardized. Copper based materials are typically utilised for the coil inside existing heat exchangers. However, on account of direct contact with the pool water, the copper based materials are susceptible to corrosion. Over time, chemicals present in the water will react with the coil, corroding and scaling the same, which may significantly reduce the life of the heat exchanger.
Liquid to liquid heat exchangers are often designed in the form of shell and tube heat exchangers. The heat exchange ability of such heat exchangers is a function of various parameters such as the length of the tubes, the flow rate of the two liquids and the material properties of the tubes.
One problem with existing heat exchangers is that they are often thermally inefficient, in the sense that it is difficult to extract a large percentage of the available thermal energy from the working fluid. This inefficiency is a result of various factors. One factor being that the two fluids of the heat exchanger are normally not in direct contact with each other, so the thermal properties of the individual components of the heat exchanger limit the thermal efficiency of the system.
In addition, in water heating applications for example, the high and low temperature fluids are only exposed to each other for a finite period of time, and this also limits the amount of thermal energy transfer that can take place within the heat exchanger.